1. Technical Field
The present invention relates to an optical disk device and an optical disk recording method, and may be used to record data onto, for example, an organic dye type recording medium such as a CD-R (compact disc recordable). The present invention makes it possible to, even if writing speed is high, accurately monitor, for example, the shape of a pit which is formed in an optical disk by selectively using light quantity detection results obtained from areas at the back side in a direction of scanning with laser beams.
2. Background Art
Hitherto, in an optical disk device, data recorded on an optical disk has been reproduced by generating a reproduction signal, whose signal level varies in accordance with a row of pits formed in the optical disk, as a result of processing a light-reception result obtained by reception of returning light obtained from the optical disk by a predetermined light-receiving element, and by processing the reproduction signal. In contrast, in writing data in the optical disk device, the shape of a pit which is formed in the optical disk is monitored by monitoring the level of the reproduction signal, and the light beam quantity is properly controlled based on a monitoring result.
FIG. 1 is a block diagram of this type of optical disk device. In an optical disk device 1, an optical pickup 2 irradiates an optical disk 3 with laser beams, receives returning laser beams, and outputs a light-reception result.
Here, in the optical pickup 2, a semiconductor laser 4 emits laser beams, and a grating 5 diffracts the laser beams to generate diffracted light beams of 0th and ±1st order. A beam splitter 6 transmits and reflects the diffracted light beams of the 0th and ±1st order which exist from the grating 5 and splits them into two beams.
A light-receiving element 7 receives the light beams transmitted through the beam splitter 6, and outputs a laser beam quantity detection result. In the optical disk device 1, driving of the semiconductor laser 4 is controlled by the laser beam quantity detection result, thereby preventing the laser beam quantity from varying with changes in temperature and time-lapse changes.
A collimator lens 8 causes the laser beams reflected by the beam splitter 6 to exit therefrom as parallel light beams. A mirror 9 causes the light beams to exit towards the optical disk 3 by reflecting the laser beams that exit from the collimator lens 8, and an objective lens 10 focuses the laser beams obtained from the mirror 9 onto an information recording surface of the optical disk 3. By this, in the optical pickup 2, returning laser beams are obtained by the optical disk 3, and the returning laser beams travel in a light path of the laser beams in the opposite direction and are transmitted through the beam splitter 6.
An adjusting lens 11 corrects astigmatism in terms of the returning laser beams transmitted through the beam splitter 6 and outputs the corrected result. A light-receiving element 12 receives the returning light beams that exit from the adjusting lens 11. In the optical disk device 1, a light-reception result obtained from the light-receiving element 12 is processed by a signal processing circuit 13 to generate a reproduction signal RF and signals TE and FE which are required for various controlling operations.
More specifically, the grating 5 is set so that, in the optical disk device 1, as shown in FIG. 2, when a beam spot SPM of the 0th diffraction light beam (that is, a main beam) scans a recording track of the optical disk 3 by a just tracking operation, beam spots SP1 and SP-1 of the ±1st order diffraction light beams (that is, side beams) are set at locations that are offset by approximately ½ track pitch P/2 in the inner and outer peripheral directions of the optical disk 3, respectively, and scan a forward location and a rearward location in the circumferential direction, respectively.
In correspondence with this, in the light-receiving element 12, the returning main beam and returning side beams are received by respective light-receiving surfaces 12M, 12S1, and 12S-1. Here, the light-receiving surface 12M that receives the returning main beam is divided into four parts by division lines in the circumferential and radial directions of the optical disk 3. Light-reception results obtained from respective areas A to D that are divided in this way are output. In contrast, the light-receiving surfaces 12S1 and 12S-1 that receive their respective side beams are each divided into two parts by division lines in the circumferential direction of the optical disk 3. Light-reception results obtained from respective areas E and F and G and H that are divided in this way are output.
After the signal processing circuit 13 has processed the light-reception result obtained from the light-receiving element 7 and the light-reception results obtained from the respective areas A to H of the light-receiving element 12 by current-voltage conversion, it outputs the light-reception result obtained from the light-receiving element 7 to a light-quantity control circuit 14 (see FIG. 1), whereas it processes the light-reception results obtained from the respective areas A to H by a predetermined computation in order to generate the tracking error signal TE, the focus error signal FE, and the reproduction signal RF.
The light-reception results after the current-voltage conversion are represented below by reference characters A to H used to represent the areas of the light-receiving surface. The tracking error signal TE is generated by performing a computation using ((A+D)−(B+C))−k ((F−E)+(H−G)). Here, k is a predetermined coefficient. By this, the optical disk device 1 generates the tracking error signal TE by what is called a DPP method.
The focus error signal FE is generated by a computation using ((A+C)−(B+D)). In the computation, the light-reception results obtained from the areas in the diagonal directions of the light-receiving surface 12M which receives the returning main beam are added, and the difference between these sums is computed. The reproduction signal RF is generated by performing a computation using (A+C+B+D). In the computation, each of the light-reception results obtained from the light-receiving surface 12M which receives the returning main beam is added.
By these computations, in the optical disk device 1 (see FIG. 1), based on the tracking error signal TE and the focus error signal FE, the objective lens 10 is moved by a servo circuit 15, so that tracking control and focus control can be carried out. A reproduction signal processing circuit 16 processes the reproduction signal RF, so that data recorded on the optical disk 3 can be reproduced.
On the other hand, the light quantity control circuit 14 controls operation of a driver 17 based on the light-reception result obtained from the light-receiving element 7 obtained through the signal processing circuit 13 in order to automatically adjust the light beam quantity so that the laser beam quantity does not vary with changes in temperature and time-lapse changes. When writing data, the light quantity control circuit 14 samples the reproduction signal RF at a timing based on a write pulse WP in order to detect the returning-light quantity that changes in accordance with the size of a pit which is formed in the optical disk 3. Further, the light quantity control circuit 14 controls the operation of the driver 17 by the laser beam quantity detection result in order to control the shape of a pit which is formed in the optical disk 3.
When reproducing data, the driver 17 drives the semiconductor laser 4 so that, by the controlling operation of the light-quantity control circuit 14, the semiconductor laser 4 emits laser beams of a certain quantity. On the other hand, when writing data, the driver 17 drives the semiconductor laser 4 so that, based on the write pulse WP that is generated by modulating data that is to be written, the laser beam quantity is intermittently set at the writing laser beam quantity.
In recent years, such an optical disk device has provided considerably increased writing speed. In the optical disk device, when the writing speed is made high, the speed of laser beams which scan the optical disk 3 is increased correspondingly. Therefore, an information recording surface reliably undergoes a thermal change in order to form a pit even by increasing the laser beam quantity and scanning the information recording surface with the laser beams for a short period of time.
However, in a related optical disk device, when the writing speed is increased, the shape of a pit which is formed in the optical disk 3 can no longer be accurately monitored, so that the light beam quantity can no longer be properly controlled.
In other words, in this type of optical disk, the temperature of the information recording surface is gradually increased as a result of setting the light beam quantity at the writing light beam quantity, so that the temperatures of localized portions of the information recording surface are increased to temperatures equal to or greater than a predetermined temperature by this increase in temperature of the information recording surface. Therefore, the localized portions of the information recording surface undergo thermal changes, thereby forming the pits. Because of this, in the optical disk, a time lag is produced from the time the light beam quantity is set at the writing light beam quantity to the time the pits are formed.
When the writing speed is increased, the speed of scanning with laser beams is increased with respect to this time lag. Therefore, before the information recording surface undergoes a thermal change, a spot of a laser beam moves, so that the shape of the pits which are formed in the optical disk 3 can no longer be accurately monitored.
More specifically, FIG. 3 is a graph showing a characteristic curve of the result of measurement of a light quantity that is detected by sampling the reproduction signal RF, when a desired piece of data is recorded onto a CD-R by successively changing a writing light quantity and increasing the writing speed by 8 times in value. According to the result of measurement, it can be understood that, at a write power equal to or greater than a predetermined power, formation of a pit resulting in a lower reflectance than that of a land is started, and a signal level of a light-reception result is reduced in accordance with the size of the pit. Therefore, in this case, it can be said that the writing light quantity is properly controlled.
In the optical disk device, when the writing speed is further increased, such a reduction in the signal level of the light-reception result caused by an increase in the writing light quantity is no longer observed, so that the shape of the pit which is formed in the optical disk 3 can no longer be accurately monitored.